1. Field of the Invention
This invention relates to a battery pack and an electronic device, and more particularly to a battery pack and an electronic device which detects a shock and disables the battery pack in a predetermined case, the battery being used in the electronic device being capable of carried.
2. Description of the Related Art
Electronic devices such as a note-type or lap-top type personal computer (notebook computer) or digital camera uses a battery (or cell), and can be brought and used in the outdoors where electricity is not available. However, it is possible that the electronic device is inadvertently dropped and a shock is given on the electronic device, when they are carried,
Thus, for example, there has been proposed that, when a strong shock is given on the mobile phone, the shock is detected to create a history of the degree of shock, the number of shocks and the like by an acceleration sensor which is mounted on a mobile phone (refer to Patent Document 1; Japanese Patent Laid-Open No. 2006-119484). Accordingly, it is possible to check a history of shock by then such as what degree of shock has been given on the mobile phone and how often shocks have been given.
When a shock is given on an electronic device such as a mobile phone, a battery pack also receives the shock which is mounted therein as the power source of the electronic device. There is no problem which has been raised by the shock given on a battery pack until now.
However, since the output voltage of a battery pack has been increased, a shock given on the battery pack has become not negligible. More specifically, a lithium-ion battery is mainly used as a battery for electronic devices such as a notebook computer or digital camera at present. The output voltage of lithium-ion battery is 4.2 V/cell, for example, being significantly high. Particularly, in a notebook computer, a plurality of lithium-ion batteries are combined to constitute a pack (a battery pack). Accordingly, the output voltage of the battery pack becomes much higher. For example, when four lithium-ion batteries are connected in series, an output voltage is 16.8 V.
I studied on a battery pack and found, when the battery pack of lithium-ion battery which has received shocks several times in the past continues to be used, the following problem may arise.
An additional shock of a certain strength is further given after shocks have been given several times in the past. In this case, there may occur a short circuit in the inside of a lithium-ion battery constituting the battery pack, and bring into fire. Also, the battery pack of lithium-ion battery for a notebook computer is constituted of an assembled battery (a combination of a plurality of batteries). Accordingly, when a shock of a certain strength is given, the balance between individual lithium-ion batteries is broken. As a result, charging or discharging phenomena may concentrate to a particular lithium-ion battery, and overcharge or over-discharge is likely to concentrate. This is very dangerous.
Thus, when a battery pack of lithium-ion battery receives a strong shock, the output current from the battery pack must be cut off, and change the battery pack to a disabled state to prevent troubles such as catching-fire caused by a short circuit in the inside of the lithium-ion battery, and overcharge or over-discharge cause by a breakdown of the cell balance between the lithium-ion batteries.